Many instruments have been developed in the past which are useful for monitoring moisture content of soil or other life-supporting compositions for growing house plants in pots, window boxes, planters, and the like. However, these instruments have proved unsatisfactory, usually for a variety of reasons. Some are so complicated and contain so many parts that the manufacture thereof makes the final cost prohibitive for amateur gardeners. Other known devices are useful initially and are simple enough in construction to make the cost low enough to make them available for amateurs, however the moisture absorption systems therein tend to become clogged, often because the capillary action thereof carries small particles of soil through the moisture paths contaminating the same, or because the moisture paths are improperly exposed to the ambient atmosphere causing the moist-dry cycle to be disturbed to the extent of providing false indications of moisture content resulting in improper watering of the plant.
With the indicator of the present invention, by contrast, an extremely simple, highly reliable, most economical, and attractive moisture monitoring instrumentality is provided. The new indicator utilizes simply formed and inexpensive materials and is so devised and configured that a proper moisture-dry cycle is established to maintain proper moisture content in the plant soil being monitored. This is achieved by providing a generally elongated housing structure formed of two opposed walls which are comprised, preferably, of a thermoplastic resin so that the opposed walls may be easily heat sealed around the periphery thereof to form a generally elongated flat-like container. Preferably, both walls will be transparent, although it is within the purview of this invention that only the front wall need be transparent.
In accordance with the invention, contained within this generally elongated housing is an elongated wick extending from one end thereof to the opposite end, and being generally of the same shape as the walls of the container. Preferably, the lower end of the housing and the wick contained therein is shaped with a generally pointed configuration, for insertion into the plant soil to be monitored. At this lower end, there is provided a bore through both walls of the housing and the moisture bearing wick, itself, for exposure of the wick to the moisture.
The upper end of the housing is generally larger and somewhat round in configuration, to form a chamber for the signal element. The center of the chamber contains the signal element which is moisture-sensitive substance, e.g., cobalt chloride, which changes color at a predetermined "break point" which is a function of its humidity. Importantly, the moisture indicating substance is surrounded by the wick in the chamber, but is not in actual contact therewith. Moreover, the wick surrounding the moisture signal element has a plurality of spaced bores or openings therethrough in registry with apertures in both walls of the housing.
These openings serve as vents for moisture contained in the chamber. Thus, moisture may be constantly removed from the indicator chamber by evaporation, the rate of which controls the moisture-dry cycle being monitored by the device. The diameter and number of openings in the wick and housing will, of course, affect the rate of evaporation. It is desirable that the upper portion of the housing be configured in the general form of a decorative flower and that the lower portion be shaped as a stem, so that the device, in accordance herewith, is aesthetically pleasing.
Before describing this invention in more detail, it may be well to note that the housing walls of the indicator herein may be fabricated from different thermoplastic resins, including, for example, polyvinyl chloride, polyethylene, polypropylene, "Mylar" (polyethylene terephthalate-Mylar is a Trademark of Du Pont), or similar polyesters. Although it is preferable to utilize a thermoplastic resin because the periphery of the container walls may be readily heat sealed together to form the container, other materials such as metal or glass, or combinations of these with thermoplastic resins may be utilized. Moreover, the wick may be comprised of a conventional felted absorbent material, such as water absorbent blotter material.
Other objects and advantages of this invention will be apparent from the following detailed description, the accompanying drawings, and the appended claims.